Funding
Active projects
What we work on
We study black holes, gravitational waves and strong-field gravity. Our work combines black-hole perturbation theory, numerical relativity and gravitational-wave data analysis, and is organised around four connected lines: the ringdown of black holes, the imprint of astrophysical environments on gravitational-wave sources, the oscillations of neutron stars, and the numerical methods that underpin them.
When two black holes merge, the remnant settles down by emitting gravitational waves at a discrete set of complex frequencies, its quasinormal modes. These frequencies depend only on the mass and spin of the final black hole, which makes the ringdown a clean test of the Kerr hypothesis. Which modes are excited, and how strongly, depends instead on the perturbation that drives the black hole.
We describe the ringdown as a spectral filtering process: the black hole selects the part of the perturbation that overlaps with its own quasinormal-mode spectrum, so the amplitude of each mode is set by the frequency content of the source. The same spectral picture explains why the late-time power-law tails predicted by Price's law are strongly suppressed for the oscillatory perturbations produced in quasi-circular mergers. We also use ringdown amplitudes and phases to build consistency tests of general relativity and searches for additional, non-gravitational modes in the signal.
Massive black holes are rarely isolated: they can be surrounded by dense gas or by dark-matter overdensities. A stellar-mass compact object spiralling through such an environment feels dynamical friction, accretion and the gravity of the enclosed matter, and accumulates a phase shift with respect to an inspiral in vacuum. For extreme- and intermediate-mass-ratio inspirals observed by LISA, this dephasing can be measurable.
We model these environmental effects and determine when they are detectable and distinguishable, using mismatch criteria and Bayesian parameter estimation. Applications include clouds of ultralight, self-interacting axion-like particles formed around massive black holes, which would allow LISA to constrain the particle mass and self-coupling through gravity alone, and the dense gaseous interiors of the Little Red Dots discovered by JWST.
Neutron stars probe matter at supranuclear densities, and their oscillation spectrum will become accessible to next-generation detectors through the post-merger signal of binary neutron-star coalescences. Mergers drive matter far from equilibrium, so dissipation can no longer be neglected.
We use a causal and stable formulation of relativistic viscous hydrodynamics to compute the oscillation modes of viscous stars. Shear viscosity shifts the spacetime modes of the star, gives rise to a new family of viscosity-driven modes with no perfect-fluid counterpart, and damps the long-lived trapped modes of ultracompact objects. This work complements numerical simulations of magnetised neutron-star and black-hole–neutron-star mergers.
Our results rely on a range of numerical tools: time-domain solvers for the equations of black-hole perturbation theory, frequency-domain methods such as Leaver's continued fractions to compute quasinormal modes, numerical-relativity and relativistic magnetohydrodynamics codes, and data-analysis pipelines for mismatch, signal-to-noise and parameter estimation. We are also exploring physics-informed neural networks as a new way to solve Einstein's equations.
Where possible, we release our codes as open source, so that the results in our papers can be reproduced.